How to find collections where an selected object is linked to?
There are at least 3 solutions:

If you select the object, go in the Properties panel &gt; Object Data &gt; Collections, you'll see the collections the object is part of:



In the 3D view if you select the object and press ShiftG &gt; Collection, it will display the collections the object is part of:



If you select the object, in the Outliner you'll see an object icon enlighted next to the collections that contain it: